text:
What does prevent installing an ADS-B transponder on a vehicle?
FlightRadar24 indicates they also track ground vehicles:

Ground vehicles visible on Flightradar24 are generally those that are most active in the movement areas of an airport, like airport rescue and fire fighting, ‘follow me’ cars, and push back tugs. At some airports, specialized vehicles like wildlife control and lawnmowers are visible.

and they show a sample:

Ground vehicle trails by FR24 at London-Gatwick, source
I wonder if it possible to install an ADS-B transponder on any vehicle?
Is it legal? Does it need a licence or some kind of activation? Assuming it is possible, would it be visible to air traffic controllers and/or show up on sites like Flightradar24?

If you are serious about finding a stolen car there are far better ways to do it.

Welcome to aviation.SE! Attaching a radio transmitter to your car would be regulated by the FCC, not the FAA, so you might get a better response on ham.SE.

I don't think this would be on topic for ham.SE either -- their area is either amateur radio practices and regulations, or the technology of radio.  This isn't really either, IMO.

Why would everybody on earth want to monitor your car?  DV, and VTC.

@MichaelHall really, turn on your telly and surf the channels. Following someones car beats nine out of ten of the shows on tv.

Good edit, voting to reopen because I have already learned something.  But the root question is still "can I used it to track my personal vehicle if it is stolen" which I think is borderline off topic.

How, exactly, is "can I install (this) radio in a car" on topic for Aviation??? Because it's a radio that is typically installed in airplanes... that makes it on-topic?

@RalphJ: "can I install (this) radio in a car". This is not exactly in the question (current version), and if you looked a bit more in depth you would probably find interesting elements for aviators. You already asked for many questions to be closed, you have the record of requests on this site by a large amount. I wonder what standard you are trying to impose. To me this question is valid, and I had a great pleasure to answer it.

@mins... I vote to keep some questions open, and I vote to close others. From what I can see, my votes are mostly in the majority - i.e. not out of the mainstream here. And when the community disagrees with my votes, that's fine too - reasonable people can differ about things. (The VTC on the question isn't a reflection on your answer, which is excellent.)

@RalphJ: "my votes are mostly in the majority", this is mathematically impossible see stats. I'm not saying you're wrong at all, just close votes are issued by the same persons and reflect the view of this minority which at times is very strict. Ping me on the chat if you want to discuss this as this is not the place here.

Use of ADB-S transmitters is limited by regulation: in the US, frequency use is limited to FCC license holders; FCC licenses are delivered only after approval by FAA, the aviation agency; FAA approves ADS-B use only for airport-based vehicles and for specific activities.
Using a reserved frequency without a license for it is indeed illegal. Therefore one could get the required equipment but is not allowed to use it.
Approved use for vehicles
From FAA FAQ:

Airport authorities or entities approved by the FAA  to use Ground Vehicle ADS-B Out Squitter Equipment are required to obtain a license to  transmit prior to operating. Title 47 CFR Part 87 governs the licensing and operation of equipment transmitting within aviation frequency bands. The applicable parts of 47 CFR Part 87  and references contained within shall be followed.

Identification
ADS-B transmits a GNSS (GPS or equivalent) position and sends it through a transmitting device, which is usually the on-board transponder also used for ATC replies and ACAS.
When installed on a ground vehicle, the equipment must fulfil the three functions: GNSS receiver, ADS-B generator, SSR transponder.
SSR transponders are given an individual 24-bit address, similar to the MAC address of network equipments, this code is delivered by ICAO. In addition crews/users enter an identifier in the ADS-B generator (flight ID), similar to a call-sign in voice communication. This ID is the one displayed by ATC equipment and tracking sites.
Frequencies
The frequencies used by ADS-B are 978 and 1090 MHz.
The latter is the one used by commercial aircraft and is actually the frequency on which all aircraft respond to ATC secondary surveillance radar (SSR) interrogations and collision avoidance systems (ACAS) aboard aircraft.
The former is used for Universal Access Transponder (UAT), which is specifically US, and used by the general aviation community to exchange data, including ADS-B messages, without cluttering SSR. Typically, ground vehicles use this frequency, possibly with a specific protocol known as vehicle movement area transponder (VMAT). VMAT equipment may also broadcast its message using a cellular network rather than by radio.

Note: There are variants for ground vehicles tracking: Vehicles can be tracked with ASDE-X, which is SSR mode X (ten), not requiring the ADS-B transponder.

Of course FAA approves the use of these frequencies only for aviation and aviation support activities. The reasons for not extending the use to anybody are pretty obvious: it would disrupt the aviation activities and pose a threat to safety.
This is similar to other uses of the "aviation bands", e.g. one can buy a VHF voice radio transmitter, but one cannot talk on VHF frequencies reserved to aviation without the appropriate license. As a matter of fact there are just a few frequencies allowed to "everyone", CB and ISM bands being the ones that come to mind. Even amateur radio transmissions are subject to a license which itself is conditioned to a specific purpose, regulation, training and exam.
Globally frequencies are allocated by the international telecommunication union (ITU), a UN agency federating all national agencies like FCC.
Visibility
Vehicles allowed indeed appear on ATC radars, on other aircraft ACAS, and on sites like FR24 which have either their own receiver network and/or have contracted for data feed with official agencies like FAA.
ICAO address registration include the type of transmitter (aircraft, ground vehicle, fixed obstacle, etc), thus any tracker may block certain types as they want, e.g. FR24 may decide to block some ground vehicles.
However for a transponder to appear on some network, its signal must be received by an antenna. While the future ATC system will be based on satellites, ensuring a global connectivity, current ATC is mostly based on terrestrial antennas, which are concentrated at or near airfields.
As noticed by @randomhead, for the frequencies considered, when antennas are on the ground they have difficulty receiving signals from transmitters also on the ground, as a clear line of sight (LoS) is generally required to get a useful signal. Devices using similar frequencies without a clear LoS, like cell phones, have been designed to benefit from diffraction by obstacles; this is not the case for SSR.
A clear LoS can be obtained for aircraft in flight, and, by multiplying antennas (including using raising multilateration techniques), for aircraft and vehicles at the airport, but for vehicles at some distance, this would require other means, currently not deployed.


text:
How do I request a frequency change to listen to ATIS?
If I only have one radio, and I'm using VFR Flight Following, what do I tell ATC when I want to pick up ATIS for the landing airport before I'm told to contact the tower?

Not a true answer per se, but a lot of radios allow you to monitor the standby frequency. Check with your radio manual to see if this mode of operation is supported.

Isn't this part of why you're required to have two radios?

@Vikki  I'm not aware of any requirement that you have two radios. Many planes only have a single radio.   Can you cite a source?

You just ask.  "[Who you're calling], request a quick frequency change to get ATIS."  Works every time.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
I have a projectile going through the air, point in front, flat plate in the rear. How do I calculate the aerodymanic forces on the rear plate?
The project that the projectile is being developed for has nothing to do with aerodynamics, but the problem is that the rear plate is being sucked off - obviously not attached sufficiently. How can I predict what the aerodynamic forces on the rear of the projectile will be? The projectile is basically a nose cone, a tube, and a flat rear end (no boat tail) that just fits into the tube.

I would say that your question has everything to do with aerodynamics, but nothing to do with aviation.  VTC.

Agree, good question, but would belong to physics stack exchange.

Ok, I'll try there. There were some other aerodynamics questions here, so I thought I'd try.

Use this diagram of base pressure coefficient over Mach. The high Mach values are from X-15 tests, the rest from a multitude of flight and wind tunnel tests. For your bullet the 3D line would be relevant; if you were looking at the blunt trailing edge of a wing, use the 2D line.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the explanation for the appearance of airplanes hovering?
A few weeks ago, I saw a plane that appeared to be hovering in the air. It was a large commercial airliner. It was not a windy day, land speeds of 24km/h max that day, about 5km/h at the time I saw it (according to meteored). The trees were not moving at all. We were not too far from the airport, it was close enough that it looked like it was landing soon. I would like to understand what I saw under these specific conditions because there is no possibility that the frontal speed was going at the speed of an airplane. What am I missing?
I of course looked it up on YouTube and found many others have seen exactly the same. For approximate height, see the following video at minute 8:22

Thank you!!!

Mentour has a very good video on the effect Here

That is actually very helpful and complete info. Will study now. Thank you!!!

You are missing perspective.
Airliners, even smaller ones, are very large relative to most flying objects we're used to seeing (namely, birds). When they are not literally on the ground it is very hard to get proper perspective on their actual speed relative to us, and it looks like they are "hanging" in midair.
In addition, planes are going their slowest speed when they are close to landing, which furthers the phenomenon.


text:
How is the voting mechanism and FDI algorithm applied in transport aircraft?
How is the voting mechanism applied in modern transport airplanes for airdata/inertial reference sensors fault detection and isolation (FDI)?
Are there any other FDI methods approved by the regulators to use on the commercial aircraft? Like Kalman filter based FDI algorithms?

For Air/IR data on Airbus see: Do redundant angle of attack and sideslip sensors use a voting mechanism, or do they display data directly? and How does the Airbus flight computer's voting system work? (for early closers, they are not duplicates)


text:
BHP increases with Altitude
Searching on internet, I found some performance charts of the Merlin Engine BHP output:

As you can see there is an increase in BHP,(mainting a constant Boost Setting), until reaching the critical altitude of the supercharger in Low Gear.
Is this increase in BHP due to a higher compression as there is a reduction in pressure at higher altitudes?
If so, should a higher IAS (Dynamic pressure) be obtained in level flight? (because more BHP are available).
Thanks for the Help!

Mechanical superchargers suffer from “throttling losses” at lower altitudes until the aircraft reaches the critical altitude where max power is created with a wide open throttle. For a detailed explanation try this video. https://youtu.be/ULLsIo1VzTw

Thanks for the answer! All clear now.

As noted in Airplane Aerodynamics by Dommasch, Sherby, and Connolly, 1967, Pitman Publishing Corporation, New York...

It is a relatively simple matter to fit to an engine a large supercharger that is capable of providing excessive MAP (manifold absolute pressure) at full throttle at sea level.  Ascent to altitude permits opening the throttle to compensate for reduction in air density without exceeding the rated MAP.  In fact, if MAP is kept constant by gradually opening the throttle as altitude is gained, the reduction in exhaust back pressure will cause an increase in airflow that actually increases engine power.  The altitude at which the throttle must be fully opened to maintain a given MAP at a given RPM is known as the critical altitude of the engine for the given RPM-MAP condition.  Above this altitude the mass air flow, and consequently the power output, diminishes because of the reduction in air density.  A gear shift providing a higher speed for the supercharger impeller, or an auxiliary stage of supercharging, simply extends the above conditions to a higher altitude.

This explanation is given and detailed on page 251 and pages following in the source given above.


text:
How does the landing gear downlock mechanism work?
How does the landing gear downlock mechanism work? Especially when it's operated without hydraulic pressure or other energy sources.
How can it keep the landing gear down and locked, during a gravity extension?

Source: smarte-webe.com

Short answer just in case details in the other answers leave anybody scratching their head trying to relate:
Think of a folding table leg with its 45 degree angled brace, and the little sliding metal bit that covers its hinge. That’s the same basic principle used in most retractable landing gear designs.

The main side brace of the gear leg is itself braced to hold it straight by the smaller brace in the middle that runs back to the main gear leg.  The smaller lateral brace has an overcenter position that locks it against folding up when compressed, same as your leg when you stand up and lock your knees all the way back.
When overcentered locked, the strut has a very shallow V shape and compression force just wants to push the strut harder into its overcenter lock configuration.  There may also be a locking pin somewhere at the point where it folds, to fully lock the strut like that as a final security for the downlock (for example to prevent tension forces from wanting to pull it out of overcenter).
There is a small actuator that drives the brace into and out of that overcenter lock position for normal extension/retraction, but when the gear is being lowered by gravity, that actuator will be idled (free to move), and there are strong springs that pull that small middle brace strut into the overcenter lock position.  It's as if someone tied a rope to your knee, and when you stood up (or if you were pulled up because your legs no longer worked), they pulled back on it from behind you to force your knee joint to go into the overcenter position where your weight can't make it buckle, and you're able to stand even though your leg muscles don't work.

You may want to add something like this image to clarify your explanation


text:
How many degrees deviation from the defined final course can I have to start the descent?
To do a VOR, ILS or RNP approach, I am turning to establish the final approach course. The approach chart shows I should descend to a lower altitude for intercepting the final descent path.
So, my question is how many degrees deviation from the defined final course can I have to start this descent?
Is 0.8 degree for ILS, 5 degrees for VOR and NDB, 0.1NM for RNP? And the same issue when intercept a VOR radial. Where can I find the official answers about those?

I think it is within half-scale deflection (whatever type of approach) and within 30 degrees heading of final approach course. [This could be wrong, I'm looking into it]. Also in what context - ICAO? FAA? EASA?

It would depend on air traffic instructions (ask), local conditions, and traffic (fly where others fly).  You are describing a common descending turn.  For final approach it would seem logical to get on the glide path ASAP, as the longer one waits, the worse it can be.

Not all courses have angular (degrees) deviation. For example, enroute GPS courses are fixed-width unlike a VOR or Localizer scales that narrow down at a fixed angle as the station is approached.

You can descend to the minimum altitude for a segment as soon as you are established on that segment.
However, I can’t find a definitive answer as to when exactly you become established. Some folks say less than full-scale deflection while others say at half-scale deflection. I’m not sure how clearly it applies, but the ACS standard is that you must maintain no more than 3/4 scale deflection, so it seems like half-scale deflection is the safest choice.

@ymb1 FAA regulation is not universal for all procedures globally. Don’t presume the person asking this is operating in America.


text:
Can I fly part 91 a German certified and registered helicopter in the USA?
Can I fly part 91 a German certified and registered helicopter in the USA?

Welcome to aviation.SE! Is your pilot's license from Germany, the US, or another country?

Yes you can.  You must, however comply with the terms of §91.711, §91.713 and §91.715, and obtain a special flight permit for the proposed operation, but it can be done.
For reference, §91.711 reads:
a) General. In addition to the other applicable regulations of this part, each person operating a foreign civil aircraft within the United States shall comply with this section.
(b) VFR. No person may conduct VFR operations which require two-way radio communications under this part unless at least one crewmember of that aircraft is able to conduct two-way radio communications in the English language and is on duty during that operation.
(c) IFR. No person may operate a foreign civil aircraft under IFR unless—
(1) That aircraft is equipped with—
(i) Radio equipment allowing two-way radio communication with ATC when it is operated in controlled airspace; and
(ii) Navigation equipment suitable for the route to be flown.
(2) Each person piloting the aircraft—
(i) Holds a current United States instrument rating or is authorized by his foreign airman certificate to pilot under IFR; and
(ii) Is thoroughly familiar with the United States en route, holding, and letdown procedures; and
(3) At least one crewmember of that aircraft is able to conduct two-way radiotelephone communications in the English language and that crewmember is on duty while the aircraft is approaching, operating within, or leaving the United States.
(d) Over water. Each person operating a foreign civil aircraft over water off the shores of the United States shall give flight notification or file a flight plan in accordance with the Supplementary Procedures for the ICAO region concerned.
(e) Flight at and above FL 240. If VOR navigation equipment is required under paragraph (c)(1)(ii) of this section, no person may operate a foreign civil aircraft within the 50 States and the District of Columbia at or above FL 240, unless the aircraft is equipped with approved DME or a suitable RNAV system. When the DME or RNAV system required by this paragraph fails at and above FL 240, the pilot in command of the aircraft must notify ATC immediately and may then continue operations at and above FL 240 to the next airport of intended landing where repairs or replacement of the equipment can be made. A foreign civil aircraft may be operated within the 50 States and the District of Columbia at or above FL 240 without DME or an RNAV system when operated for the following purposes, and ATC is notified before each takeoff:
(1) Ferry flights to and from a place in the United States where repairs or alterations are to be made.
(2) Ferry flights to a new country of registry.
(3) Flight of a new aircraft of U.S. manufacture for the purpose of—
(i) Flight testing the aircraft;
(ii) Training foreign flight crews in the operation of the aircraft; or
(iii) Ferrying the aircraft for export delivery outside the United States.
(4) Ferry, demonstration, and test flight of an aircraft brought to the United States for the purpose of demonstration or testing the whole or any part thereof.
§91.713 reads:
No person may operate a civil aircraft of Cuban registry except in controlled airspace and in accordance with air traffic clearance or air traffic control instructions that may require use of specific airways or routes and landings at specific airports.
And §91.715 reads:
a) Foreign civil aircraft may be operated without airworthiness certificates required under §91.203 if a special flight authorization for that operation is issued under this section. Application for a special flight authorization must be made to the appropriate Flight Standards Division Manager, or Aircraft Certification Service Division Director. However, in the case of an aircraft to be operated in the U.S. for the purpose of demonstration at an airshow, the application may be made to the appropriate Flight Standards Division Manager or Aircraft Certification Service Division Director responsible for the airshow location.
(b) The Administrator may issue a special flight authorization for a foreign civil aircraft subject to any conditions and limitations that the Administrator considers necessary for safe operation in the U.S. airspace.
(c) No person may operate a foreign civil aircraft under a special flight authorization unless that operation also complies with part 375 of the Special Regulations of the Department of Transportation (14 CFR part 375).


text:
Why aren't the 'White shirts' in charge of removing the arresting wires on an aircraft carrier?
I understand that the green shirts are in charge of catapult maintenance, but why are they the ones that remove the arresting cable on US aircraft carriers? White shirts are the landing officials, so why aren't they in charge of removing the cable? Also, could you clarify the process of removing the arresting cable? I downloaded a pdf explaining the meaning of the jerseys, but it didn't clarify this question. Thank you.

The "why" would presumably be because that's the way the Navy has split it up. Or, because the White Shirt is doing something else at that particular moment, like talking the next guy in. Doesn't necessarily need to make sense, it just "is".

Other docs describe green shirts as "running and maintaining catapults and arresting gear" so presumably they are not only in charge of unhooking the cable but hooking it up ready for the next guy. Makes sense not to have to hand it off to another team.

And the white shirts you are talking of actually guide the landings, which is a very important and difficult job requiring lots of training. After the plane has landed they are getting ready to land the next one, and won't be rushing off to unhook anything. (There are also lots of other "white shirts" but they also have specialized functions.)

To build off of your comment, I found this resource: https://www.history.navy.mil/content/dam/nhhc/news-and-events/multimedia%20gallery/Infographics/FINAL_RainbowJerseys_highres_PDF.pdf . It explains that white shirts are in charge of quality control, landings, liquid oxygen, safety, and medical needs aboard the deck

The white zone is for loading.

Don't tell me which zone is for loading and which zone is for parking @mins!

Why the two dowvotes and close votes?

The simple answer as to why "white shirts" don't remove the cable is that the Navy, like any organization, assigns duties based on skills and training.  The skillsets required for catapult and arresting gear maintenance are similar, so it makes sense that personnel preforming these duties are lumped together in the same functional group.
I believe the "landing officials" you mention is referring to LSOs, or Landing Signals Officers.  (I was one once...)  LSOs are pilots first, assigned to deployed squadrons, who fly regularly but also receive specialized training on the intricacies and dynamics of recovering aircraft at sea.  Every fourth day during flight operations the LSOs will stand duty on the flight deck.
Interestingly, white shirt personnel are not interchangeable like some others are.  While most shirt colors contain groups of personnel trained in the same occupational field, white shirts are actually a catch-all color for other miscellaneous flight deck personnel.  For example, LSOs just happen to wear white - that doesn't mean we are qualified to fill a medical or QA role, or replace liquid oxygen bottles.  Those tasks require similarly specialized skills and training.
Of note, if you look at photos or videos of LSOs you may note that some are in Khaki trousers with white turtleneck flight deck jerseys and float coats, while others are in flight suits.  The team on duty generally wears the khaki and white, but there are often LSOs in training up there to observe, and sometimes you will be scheduled to fly on a duty day, hence the mix and match of uniforms.
Now, let's get to the process of "removing the arresting cable".  This could be interpreted a couple of ways as the comments indicate.  If by this term you mean unhooking the cable from the aircraft tail hook, this doesn't require a person to go actually manually unhook it.  The way it works is as follows:

Once the aircraft is at a full stop the pilot is signaled by a yellow shirt, (aircraft director) to throttle back to idle and release brakes.

A signal is then given, (and seen by the pilot) to "pull back" the cable.

A hydraulic pump is activated by deck edge personnel and the arresting gear cable begins to retract, pulling the aircraft to the rear.

Once the aircraft has a little rearward momentum, the director signals for arresting gear retraction to temporarily halt while the aircraft continues to roll backwards.

As soon as the hook is clear of the wire the pilot is given the hook up and taxi forward signal.  The gear is then fully retracted into battery for the next landing.

If, however, by "removing the cable" you meant physically removing and replacing what we call the CDP (for Cross Deck Pendant) because it has become kinked or has broken strands, (my first interpretation) well that is a different process entirely.  And it's one that happens amazingly fast during the heat of a flight operations with potentially low fuel state aircraft in the pattern overhead.
If a CDP cable takes a couple hard hits and is deemed unserviceable:

Two green shirts will run out to disconnect it, drag it to the side, and pitch it overboard.

Two more will follow on their heels with a new one from the spares along the starboard side, and hook it right up to the fittings at the end of the spools below decks.

If done correctly, (within a minute or two) sometimes only a couple planes may need to be waved off for a foul-deck before the recovery cycle resumes.

Replacing a CDP is dirty, nasty, work.  The cables are loaded with grease, and if frayed may have sharp strands of metal.  When done efficiently it happens fast, like a racing pit stop...  And it would make as much sense to pull an ungloved, specialized Pilot/LSO off the platform to do it as it would to have a NASCAR driver jump out of his/her race car to fill it with gas during a pit stop, or expect a major airline captain to stop and change a tire in the midst of doing cockpit pre-flight checks.


text:
Why are the cargo doors of the C2 Greyhound open during flight, even when not delivering cargo?
You may find this strange, but I have a love for the C2 Greyhound and E2C Hawkeye. I noticed that when flying, the C2 Greyhound often opens its cargo doors. Is this for a better view, training, or other reasons? Thank you.

Where have you observed this?

This video: https://www.youtube.com/watch?v=IAGEu_X_zoo

And this one: https://www.youtube.com/watch?v=48jZgc1-O-o

It's clear in both those videos that the doors are opened for the benefit of the cameras. I don't think you need look further than that.

Thanks for the clarification Linus. I would point out that two videos do not constitute "often", but rather "sometimes" :) Youtube and other such media seldom present run of the mill operations, the usually focus on some kind of special shenanigans.

I think that they just did this for air to air photography. I just did some research, and the only reason I could find was for airdrops.


text:
Why doesn't the US Navy utilize seaplanes?
I understand that seaplanes are usually prop planes but for cargo planes it would be beneficial in times where large cargo supply operations need to be carried out on non-carrier operations.

https://warontherocks.com/2020/07/bring-back-the-seaplane/

If you want to see examples of commercially successful large seaplanes google Saunders-Roe. They were the kings of seaplanes in the 40s and 50s. By the 1960s they shut down.

The real answer is because there is no need.
Prior to WW2, both the US Navy and US Army had huge interest in seaplanes for exactly the reason you mentioned: large cargo supply operations. Indeed, it was not only the military who were interested. Commercial civil aviation was also hugely interested in seaplanes. The period in history that saw the success of large seaplanes was exactly at the beginning of WW2.
WW2 had a very interesting side-effect to aviation. Because aviation was so important in the war effort the war caused thousands of airfields to be constructed. After the war a lot of these airfields evolved into airports (both military and civillian). Airports killed seaplanes. The main advantage of a seaplane is being able to operate without an airport. If you have an airport you don't need seaplanes.
WW2 also taught militaries around the world the importance of combined arms and cooperation between all the different forces you own. For the US military transport operations are primarily the responsibility of the Air Force. So the reason why the Navy does not do large cargo supply operations is because that is the job of the Air Transport Command which is part of the Air Force. And the US Air Force does not want to use seaplanes to transport cargo because they have airbases all over the world.
There is practically no location on Earth near a large body of water that is not also near an airport or airfield.

How about small bodies of water- any where not near an airport or airfield?

@user2617804 The US Navy does not operate inland. That's the domain of the Army and they have Chinooks and Blackhawks for such operations so they don't need the small body of water when they can land cargo directly on mountaintops.

What fraction of islands and atolls in the Pacific have airstrips large enough for big cargo aircraft like the C5 Galaxy? What fraction of the water in such island chains? I think you meant to say “no LAND location on Earth near a large body of water is not also near an airfield”, since not true for ocean surface, which by definition are near, actually part of, a large body of water.

They can also land C130s and C-5 galaxies on relatively flat terrain on short runways as well as beaches. There was an operation to rescue hostages in Iran that had 4 c130s fly ahead to refuel helicopters on the ground.

@KrazyGlew There are actually quite a few islands in the South Pacific that operated airbases in WW2 that could probably be reactivated fairly quickly. However, this is no longer how the US military works. These days the US will call in favor from surrounding countries. For example during the Korean and Vietnam wars the US initially operated from Japanese islands and the Philippines. During the Iraq war the US initially operated from Jordan and Saudi Arabia. The US can use its economic power as a weapon. This is partly why the economic rise of China is seen as such a strategic threat

The C-130 can land just about anywhere that there's dirt.

@BobJarvis-ReinstateMonica The C130 can't quite cover Pacific operations. The C17 Globemaster however can fly from the continental US to Hawaii and from Hawaii to either mainland Asia or New Zealand. It can also operate from almost any airfield the C130 can

Very good answer because in fact, there were prior to WW2 efforts to construct big floatplanes barracks close to capital cities. It was just replaced by airports

Because you can't land a seaplane at high seas anyway. Seaplanes can't handle too big waves.
It is said that hitting water at high speed is just like hitting concrete (at somewhat slower, but still quite high speed). The landing has to be gentle for the sea plane to handle it (about similar to landing on the land). But if there are significant waves, the aircraft touches down, bounces of the next wave and then will hit the next one at too steep angle and be damaged or destroyed.
With early float biplanes that had landing speed maybe 20 or 30 knots it could work, and they were sometimes used as observation planes launched with catapult and then landing on the water next to the launching ship. But today wherever slow speed is enough, a helicopter is more practical, and when high speed is needed, it wouldn't work.
And the Navy did try with Convair F2Y Sea Dart, and it proved impractical. It was also other parts of that design that were unsatisfactory, but nobody ever try the water skis again because they didn't show enough advantage to be worth it.
Also Russian Navy tried with Beriev A-40 Albatros, with original intent as maritime patrol aircraft, but the only version that entered production is the civilian Beriev Be-200 Altair used mainly for aerial fire-fighting.

In a comic series called Tintin, he used a catapult seaplane but if you look at the Boeing Pelican Prototype, I believe there could very well have been a seaplane variant

And now they have the V-22 Osprey anyway, which covers all the space a naval cargo seaplane might.

@Harper-ReinstateMonica, indeed. And I didn't think it would, but a V-22 has double the payload compared to C-2 Greyhound, so it certainly solves the problem pretty well.

In addition to Jan's answer, to recover the aircraft you need to slow down, nearly stopped. This makes the entire ship group vulnerable.
Also, an aircraft carrier can recover aircraft at full speed and have multiple launch/recovery operations running at the same time. Swapping out a flight of aircraft takes minutes.
For cargo operations this is called "replenishment at sea" and there is a well defined method to carry that out without stopping or slowing down much.

My understanding was that carriers actually prefer to be moving during launch & recovery, since sailing upwind increases the airspeed relative to the deck.

@MichaelSeifert Not just preferred, they are required to. Landing speed would be way too fast if the carrier were stopped, the arresting gear wouldn't be able to stop the aircraft. That 30+ knots of speed means a lot.

Para 1:  It took a couple reads of the first paragraph to realize you meant to recover the seaplane.  (I thought at first this contradicted para 2)  Consider clarifying.  Para 3:  The Navy actually calls it UNREP, for Underway Replenishment of fuel via hoses between ships, or VERTREP, for Vertical Replenishment for helo transport of cargo.   The COD is just the COD, I have never heard it referred to in more formal terms as you described it.
Your comment:  I believe the C2 can recover with very a slight tailwind.  (I can verify if needed...)

I had about 1,800 pilot hours in seaplanes.  Seaplane ops were very costly in equipment and manpower plus the eventual salt-water damage to the planes.  The sooner we could end those ops the better.

authors: Bob Jarvis - Слава Україні


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Why do the replacements for craft like the C2 Greyhound and E2 Hawkeye still use turboprops?
These two airplanes are some of the classics in naval history, but replacements for them exist. When taking a look at them, they do have some improvements, but I still have one question. Why do they still use turboprops? For the Hawkeye, is it for stronger signal strength? I could understand that but wouldn't it be better for the Greyhound to have jets as it is a supply craft?

Turboprops excel at lower and slower speeds, which, it seems is what the Navy wants for its COD operations. According to Wikipedia, the replacement (by 2024) for the C2 will be the CMV-22Bs - a Navy version of the Marine's V-22 Osprey - another prop driven aircraft.
As you've noted, both the C2 and E2 have undergone extensive upgrades since they first went into service. However, the majority of the upgrades have been avionics and electronics, with (again according to Wiki) one engine upgrade for each aircraft and some airframe updates.
As to "why", it's because the Navy has prioritized electronics and airframe upgrades over engine upgrades. Also, as I understand it, going from a turboprop to a turbojet/turbofan involves significantly more than just adapting the engine to fit the mounting pylon (or vice versa), and the Navy obviously feels that the money to do so is better spent elsewhere.

The replacements still use turboprops, because turboprops are superior for the mission that both the C2 and E2 carry out.
Image Source
The E2 is a radar-in-the-sky, and loiters above areas to be monitored. High airspeed is not part of the design package for this mission, endurance is. Low fuel consumption per hour increases loitering time. Same goes for the AP-3C, which after switches off 2 or 3 of its engines during missions.
Image Source
The C2 is the freighter/supply version of the E2. It fits within aircraft carriers (the reason for the multiple short vertical tails) and its mission is to carry supplies over the longest range possible for a given airframe. Low fuel consumption per kilometer.

So both types benefit from low fuel consumption. The graph above is from Torenbeek, Synthesis of Subsonic Airplane Design, and compares hourly fuel consumption at a given drag for different propulsion configurations. At lower speeds, the propeller graphs are vastly superior. Only when supplies are always required in a hurry, would it be beneficial to mount turbofans on the C2. The E2 would always have less loitering time with turbofan engines. Plus mounting the same engines on both types provides commonality and reduces spare part count on board.
So why are turbofans not considered for the replacements? Because they are not beneficial to the aircraft mission.

This combines with another thing: the minimal speed rises with the optimal cruise speed, and lower landing speed means the arresting gear can stop, and the catapult launch, a larger weight. For supply aircraft the slower speed is worth larger payload.


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As a US citizen living in Europe, must I use a trust as the owner of an N-reg aircraft?
I have found lots of information online about European pilots owning and flying N-reg aircraft using trusts set up in the US. I live in Europe, but I'm a US citizen, so must I also set up a trust because I don't live in the US? I cannot seem to find a definitive answer on this with references to supporting regulation.

As a US citizen you can own an N-reg aircraft directly, regardless of where you live. The regulations on aircraft registration are in 14 CFR Part 47. They say who can register an N-reg aircraft, but they don't say anything about where that person must be. 47.3(a)(1) simply says:

§47.3   Registration required.
(a) An aircraft may be registered under 49 U.S.C. 44103 only when the
aircraft is not registered under the laws of a foreign country and is—
(1) Owned by a citizen of the United States;

The regulations are summarized in a more readable way on this FAA site. A trust allows a non-US citizen (or non-resident alien) to own an N-reg aircraft provided they have no more than 25% of the voting rights in the trust, per 47.7(c)(2)(iii).

No, as a US citizen you do not need to jump through any hoops to register an N-reg aircraft in your name, anywhere in the world. It doesn't matter where you live. I used to own an N-reg aircraft when I lived in Germany. It was registered to my German address. When I moved back to the US and brought it with me I submitted a change of address, and that was the end of that.

According to NBAA, trusts are used by non-US citizens to register aircraft with the FAA. Because you are a US citizen, it looks like you don't need a trust to maintain the FAA registration. Here's the article with references to the FARs: https://nbaa.org/flight-department-administration/aircraft-registration-transactions/owner-trusts/ . Here's an aviation trust company: https://aviationtrust.com/ . I have no financial interest in that company. They appeared higher up in my search.


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What are the EASA external aircraft lighting requirements for day/night/VFR/IFR operations?
I have attempted to decipher the EASA rules related to non-commercial small aircraft external lighting requirements (for a pilot) for the various types of flight, and I can only find the MEL for complex aircraft.  Can someone point me to the requirements?


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Why does the elliptical wing planform have two different types of curves?
Generally, I have seen that the planform of an elliptical wing consists of two different types of elliptical curves
The elliptical curve towards the leading edge has a lower value for semi-minor axis and the curve towards the trailing edge has a higher value of semi-minor axis
What is the reason for such a geometry?
(Image is attached for reference)

It's because the center axis for the ellipses has to be along the thickest section of the wing, because there is also a taper in thickness that must be accommodated as the ribs get smaller and smaller toward the tip.  In your sketch, the thickest section is at 40% of chord and the taper in both planform and thickness must be oriented to that 40% chord line, hence the asymmetrical curves.
The placement of the axis of maximum thickness is a function of the particular airfoil selected, that is, the point of maximum thickness of the airfoil section itself.  For structural efficiency, this is normally also the location for the main spar. In the sketch, which resembles a Spitfire wing planform, the broken line will be more or less the main spar location, with the nose ribs on the left and the main ribs on the right, with the ellipse curves placed to maintain the 40% forward/60% aft ratio out to the tip.
If the thickest section of the wing was at 50% of chord, then the ellipses would be symmetrical.

You might also note that it is easier to construct a wing with a straight main spar than one which is curved.

I assume you mean curved as in the upper and lower caps having a curvature toward the tip to be in conformance with the ellipse of the planform.But the caps on a Spitfire spar are straight, not bowed and it lives with that imperfection for ease of manufacture.The difficult part manufacturing wise is the ribs with each having a custom profile with complex flanges to mate to the skins properly, and the need to form compound shapes in the leading edge skins, requiring them to made on a stretch press, or stamped in parts and welded together, then heat treated, instead of a simple single wrap bend.

What I mean is if the wing were a perfect ellipse then the main spare would have to curve backwards which is harder to make compared to a spar that is straight. I'm the upvoter so I like your answer, but I thought that the manufacturing difficultly of a compound curved spar is part of the reason for keeping the thickest part of the airfoil in a single line.

Oh I see what you mean.  It would be more correct to call it a 'double semi-ellipical" wing I suppose.

Makes complete sense.
So, the center axis should change according to the maximum thickness of the airfoil and the ellipse should be designed accordingly. Understood.


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How does a jet engine burn fuel when it is not on an afterburner?
I understand the idea behind afterburner as fuel is added to the exhaust to increase the mass and expansion of gasses to increase the thrust, and that explains (in very obvious way) how the fuel is burned when a jet engine is on an afterburner.
However, when the jet engine is not on afterburner, where and how the fuel is burned? This NASA article describes "there are as many as 20 nozzles to spray fuel into the airstream. The mixture of air and fuel catches fire". So does it mean there are two separate phases to add fuel to airstream, first (compulsory) for the normal operation and the second (optional) for the afterburner?

It's called "afterburner" because it comes after the burner.

related https://aviation.stackexchange.com/questions/71301/what-is-the-difference-between-turbojet-and-turbofan-engines/

@Therac I don't think so. It's called “afterburner” because it's a burner that comes after the turbine. (Which itself is, sure enough, after the main burner, but the name of the afterburner doesn't imply the presence of that.)

@leftaroundabout Don't spoil the pun. And still, it is called "afterburner" to distinguish it from the primary burner. Otherwise it would just be the burner. Which itself comes after the compressor, but no one calls it that.

In the beforeburner.

The regular way to burn fuel is not to use an afterburner. The afterburner is an option added downstream of a regular engine to increase its thrust temporarily. It is an interesting alternative to fitting the aircraft with a larger engine. However the additional thrust it delivers is very expensive.
The normal way to burn fuel involves a combustion chamber fed by an air compressor. The afterburner is able to work without a compressor because it uses air from the engine upstream.
I'll split my answer in two sections: The regular combustion chamber and the afterburner.

1. Regular combustor, e.g. for a turbofan
There are four steps in the jet engine, each occurring in a different section:

Air compression in the compressor.
Air and fuel mixing in the combustion chamber, and mix combustion.
Hot gas expansion in the turbine to produce power.
Gas release in the exhaust.

In addition this engine, which is a turbofan, has a large fan to create thrust. A fan is like a propeller. From left to right: fan, compressor, combustion chamber, turbine, exhaust:

CFM56-5 engine, source
Air is compressed in order to store a large quantity to allow more fuel to be burnt. The more fuel burnt per unit of time, the largest the power of the engine.
Air and fuel are injected in a combustion chamber, which can be of several types, in this example this is an annular duct with individual fuel nozzles.
Each fuel nozzle sprays fuel in an area of the chamber. Air from the compressor is directed to this area to create the mix. Combustion occurs in the annular duct.
There are igniters to start the combustion, then gas continuously burn and as the temperature is extremely hot (1,700°C for this engine), combustion is spontaneous. Igniters can then be turned off, maintained active, or set to be reactivated automatically in case of flameout (choice from the crew).
The annular duct is made of liners with hundreds of holes. Air also enters the holes to create swirls in the combustion chamber and improve fuel dilution, and to cool the liners as this section is the hottest of the engine and materials are close to their temperature limit.

CFM56-5 engine, source
Gas produced by the combustion is directed to the turbine stages. The turbine spins, moved by gas velocity. The turbine role is to extract energy from hot gas to rotate the compressor and the fan.
In this engine the fan just pushes air rearwards. This accelerated air creates thrust by reaction (80%). A small amount of thrust is also produced by the core engine when gas is released in the exhaust (20%).
A more complete explanation in this video. Detail of the combustion chamber:

Combustion chamber CFM56-3, source
2. Afterburner (post-combustion)
The afterburner is a second burner, but it works only in the hot flow of a jet engine upstream, it is a complement to this engine.
Afterburner rational
As shown in Nasa slide provided in OragnicMarble's answer, thrust in aero-engines is created by increasing air momentum, the product of mass by velocity. It doesn't matter if a large mass is accelerated by a small amount, or a small mass is accelerated by a large amount. However accelerating by a small amount if economically more efficient, that's why manufacturers use a larger fan to produce a larger thrust rather the same fan with a higher velocity.
There are cases where an additional thrust is required only at specific times, and where a larger engine is not desirable (weight and size). For them it makes sense to increase air velocity a bit more, and keep the mass unchanged. The afterburner shines in this niche.
The principle is to take the mass of gas after the normal engine exit, and re-heat it to increase its pressure. Energy is again fuel combustion with oxygen still present in the gas. The compressor is not required to increase the mass of air to be burnt. As there is no compressor, the turbine can be removed too. So in effect an afterburner is a very simple solution.

Engine afterburner concept
This additional heat expands gas, increasing its pressure, and a second nozzle converts the additional pressure into velocity.
Afterburners have many cons: Noise, flame and inefficiency (around 5 times more fuel than a regular combustor). They are not used in civil aviation, except on the Concorde and Tu-144, the only supersonic civil aircraft. Post-combustion was used for takeoff and to accelerate to supersonic speed.

Afterburner on Olympus 593 engine (Concorde), source

The Tu-144 was another civil supersonic transport and used afterburners as well.

This doesn't seem to me to directly answer the question - what makes the fuel/air mixture burn in the annular duct?  Are there spark plugs/a pilot light/something similar?  Or does the fuel spontaneously ignite due to the air temperature being hot enough from compression?

I question the repeated statement that the afterburner accelerates the exhaust gases to supersonic speed.  I understand that this is being written for introduction purposes, but it's really the nozzle's job to do that acceleration, right?  The afterburner is supplying the energy to do that though

@ErinAnne: Yes the afterburner, commonly called "reheater" just heats the gas, its expansion and the nozzle do the rest.

@AndrzejDoyle: I've updated the answer. In the engine shown there are two igniters (redundancy). Ignition is required to start the combustion and is then usually turned off, and reactivated automatically by the FADEC in case of N2 power loss (flameout).

So - why did the SR71 stay on afterburner all the time ?   Or were was it just equipped with a "second-stage combustion chamber"

@Criggie: That could be a good new question as the J58 engine has a unique design worth a full explanation. The afterburner worked like described at lower speed, but the SR-71 switched to turbo-ramjet mode for supersonic cruise. In this mode the unusual ramjet is a made of the compressor and the afterburner, but it's a full new type of engine. Ramjets, like afterburners, burn a lot of fuel. Some details in this answer.

Another NASA article shows you the diagram you need.

You can see the two places fuel can be injected, before and after the turbine. As you say

there are two separate phases to add fuel to airstream

The basic answer is yes.  Fuel is burned in the main section to make thrust (and drive a fan in that kind of engine), and keep the compression/combustion cycle going, and to work properly (not melt itself), most of the air that got compressed by the compressor section is used to control the flame boundaries within the burner can and cool the engine. Maybe only a 3rd to half of the mass flow entering the burner can in the core engine actually gets burned, that is, has its oxygen consumed; the rest is for flame control and cooling and is mixed in with the burnt air going into the turbine.
So the air leaving the turbine section of the core engine still has most of its oxygen content.  The afterburner just takes advantage of this by dumping more fuel to use up the rest of the oxygen and get a thrust bonus while the air is still compressed. An afterburner is kind of a ramjet stuck on the end of the normal engine, except it doesn't need high speed to get the ram effect; the main engine is providing the ram effect as well as sufficient oxygen to make it work.

+1 for mentioning the over-lean fuel mixture in the core leading to oxygen remaining in the exhaust after the turbines.

So does it mean there are two separate phases to add fuel to airstream, first (compulsory) for the normal operation and the second (optional) for the afterburner?

Yes.
The key difference is that the regular burner is between the compressor and the turbine, but the afterburner is the last item at the back of the engine. That means that the regular burner has to operate at a temperature that won't destroy the turbine. This means that jet burners run lean, the exhaust gasses sill contain a lot of oxygen.
Afterburners can run much hotter which which means higher thrust for a given size/weight of engine. The trade off is that their fuel efficiency is awful.


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Switching careers from physics to aviation
The main question is whether the background in the (scientific) field of applied physics and engineering can help one to start a career in aviation (to do it for living)?
It seems impossible and not worth trying, because it looks like many airmans start flying from the very beginning of their lives. After 15 years in the air they are (al least looks like) mature pilots that would be chosen to be hired somewhere instead of "that freshly switched street bum".
On the other hand, that sort of fundamental education and some years of work in the field may pose some advantage. Does it, really? If yes, how can it be exploited?

Your assumption about pilots starting out young is wrong. I know many who started later in life. In fact COVID has shown that the wise move is to develop a backup career before becoming a pilot.

Hi @StaticZero, your question specifically uses the word aviation, so does that include work other than that of a pilot?

It's one of those things about the flying game that the actual details of previous education and experience outside of aviation count for relatively little, other than what they may indicate about someone's personality, worldview and leadership potential going forward.  This is because the knowledge base and skill set are unique to the trade.
I used to know a Capt of a major carrier who was on a selection board, and he told me once that the only real reason airlines expect a university degree is that it provides a higher than average probability that a candidate will be able to handle the firehose flow of information that a pilot has to deal with on an initial type course.  What the degree was actually for was not that important as long it was demanding to some extent (not those "XXX studies" degrees).
If someone is hiring a pilot, they want to know about flying experience, personal attitude, character, and very importantly, leadership potential (since in the long run they are expecting the candidate to be in command of a crew at some point).  Previous non-aviation experience that establishes strong leadership potential (the leadership ideal fostered by Crew Resource Management theory specifically) probably has a stronger effect on your desirability as a candidate that any particular technical background.
Now, if you get into a flying career and at some future point, where you have ample flying experience, you apply for a job posting for, say, a production test pilot with an OEM, or something similar at an airline, which is likely to have a dual engineering/flying function, then the physics/engineering background might count for quite a lot.
But at the start, it mostly indicates to a potential employer that you have an above average ability to absorb information, so it can't hurt, but don't expect much more than that.

I'd say (from experience) that a related degree can certainly help to pass theoretical exams. (In some bad cases, it can even hurt when you know more than your examiner). But this mostly applies at very early stages, for initial training.

Yeah could say that's related to the "absorb vast amounts of information" angle.  People with technical/scientific degrees also tend to have training that makes them very methodical in absorbing and processing information. Across the broader culture, the need for a degree to confirm a minimum level of intelligence followed from the ending of the practice of companies using "aptitude" (IQ) tests on employees to select candidates for advancement and training (automakers would select candidates for their internal engineering schools this way), following several civil rights lawsuits in the 70s.

This question is prolly getting closed as opinion based, but meanwhile I will try to give you a somewhat-of-an-answer (an opinion, if you will):
If you are asking about becoming a pilot, having a prior education will not harm you. The selection processes involved in pilot career path are, however, very complex, and involve many considerations that might not be obvious at first glance.
While successfully performing the duties of a pilot in command of a modern aircraft does require above average intellect (yes, I dare say so), there is such a thing as being too smart for the job (yep, I dare say this too). The skill set of a professional pilot is a mix of high and steady cognitive performance across a very wide range of circumstances, ability to easily adopt new information, to resolve problems under extreme mental load, good motor skills integrating well with preferably above average sensory capabilities.
Your education and career as a physicist (?) does portray you as a person with the ability to absorb and process difficult concepts, but there is so much more that your employer is looking for, so it hardly is a deal breaker, one way or another. I know pilots with former or parallel careers as engineers, doctors, CEOs, architects and so forth. You name it, they got it. As long as you are not the garden variety Einstein, it's unlikely your intellect will be seen as a problem.
Other aviation careers do not differ much in general sense, unless of course the career you are thinking of specifically can make use of your special skills and knowledge.
P.S. I just noticed John K had already posted an excellent answer, pretty similar to this one, but I'm not gonna let my typing go to waste :)


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What is the risk of leaving the MAN START PB 'ON' on the A320?
During a manual start on a A320, the ENG MAN START P/B opens the start valve which then runs the starter motor. During the MAN START process, at some point, the start valve closes automatically. What are the risks associated with continuing to leave the MAN START P/B ON at this point?

Well, documentation is a bit vague about this, and I suppose a technician would know more about the different things the ENG MAN START bp is doing, but from a quick glance at the FCOM there is one major difference that I can spot:

[The FADEC durring a manual start]  (...) Closes the engine start valve, and cuts off the ignition when N2 reaches 43 %.

Bold emphasis is mine, no other conditions except N2>43%.
Leaving the ENG MAN START pb on means FADEC keeps assuming we are trying a manual start, and will cut off ignition anytime the N2 is above 43%. No prob as long as engines are running, right?
But that means (I assume) when you then enter turbulent/stormy weather in flight and turn on  IGN/START to prevent a flameout, nothing happens as FADEC is happy that N2 is above 43% and you manual start has been ‘succesfull’.
I don’t really know if it will even attempt an auto restart when you get a flameout, as the N2 will probably keep windmilling for some time depending on your airspeed, so you could end up with a big problem.

From a technician standpoint, your answer is very close. I can’t give an official answer because I don’t work the A320, but these systems are pretty standard on any jet. Starter cutout on most aircraft engines is usually somewhere between 42-50%. In the case where starter disengagement fails to happen, you don’t have long before the starter shaft shears - which will usually happen somewhere in the ballpark of 55-60%. If you want to make friends with your local mechanic, this is not the way to do it. In the rollback scenario, engines should automatically “continuously relight.”

To my understanding, the input from the MAN START switch (a ground/open discrete into the Engine Interface Unit), is only taken into account by the FADEC logic if the engine is not already running. Once the engine control logic goes into running mode (i.e. N2 rises above idle), it will stay in that mode until the engine master lever (EML) is set to Off, regardless of whether the engine is lit or not.
In other words, once the engine has started, the position of the MAN START p/b is irrelevant, even if the engine flames out (however, note that the FCOM procedures for engine failure often call for the EML to be set to Off, at which point the position of the MAN START switch comes to play in any subsequent attempt to relight the engine).
One risk I can think of is that if you are on the ground, shut the engines down, or even power off the aircraft, then when you power everything back on and attempt to start an engine (i.e. turn the engine start selector to IGN), the autostart procedure will be inhibited by the MAN START switch being already on, and the FADEC will go into manual start mode instead.
If you then immediately set the EML to On (which wouldn't be a problem during a normal autostart), fuel would start to flow right away, while the engine may still be below the required minimum N2 for fuel admission (16%), therefore the engine could fail to start or worse (an engine fire).


text:
Does FAA or EASA has any requirement for Supervised Take off and Landing?
India has a regulation of conducting supervised Take off & Landing. Same requires particular experience for Captain and First officer. Is there any similar requirement in FAA or EASA?

Related: How common are regulations limiting when the FO can be PF?

Can you cite this regulation so we can look up anything comparable in EASA or the FAA FAR's?

@RonBeyer: It should be this one, linked in the related question

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Are VOR frequencies static?
I am a brand new student pilot pursuing my private cert.  I don't need to know this for a while, but I'm trying to learn about VOR navigation to enjoy my sim flights more, in the meantime.
My question is this: is the VOR frequency for a given station static/permanent?  If you're looking at a chart from ten years ago (which, granted, I'm sure you're not supposed to be doing) and it shows a freq for a given station of 116.20, is that frequency likely to still be 116.20 for that station today?
That's a bit exaggerated of a timeline, but another way to ask this question is this: how often do VOR frequencies change?  How recent does a chart have to be, for you to rely on a frequency as printed on that chart?

FYI, VORs use frequencies in the very high frequency (VHF) band from 108.00 to 117.95 MHz.

I don't have evidence or official source for this, but my experience is it almost never change. However speaking of old aviation charts, the radials do change due to magnetic variation - if something is 253 degrees ten years ago, it could be 258 degrees now. If it is a runway, it would be RWY 25 back then but RWY 26 now.

I can point to A LOT of VORs that have had the same freq for >15yrs.

Charts are updated regularly by the FAA and expired charts should not be considered legal for navigation. Your chart must be current as per the date range printed on the cover for it to be considered reliable. That being said in my experience the VOR frequencies remain constant although I'm sure you can find instances in which they have changed over the years I have yet to see it happen.
FWIW the FAA is slowly shutting down the VOR system as GPS has become the prevalent navigation method.

When there has been interference issues, VOR frequencies as well as LOC frequencies have been reassigned.
However, as a general rule, they remain static for decades.
I have charts from the 40's and 50's and many of the VOR and NDB frequencies have remained the same.  EXCEPT that the NDB frequencies are almost all decomissioned, at least in my area.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Aclad sheet metal P/N 22024T3
I am looking for aclad sheet metal  P/N 22024T3   2MM, 1.2MM AND 1.6MM 1 SQM each. Anyone could help me locate those? I sent requestes to MROs etc, most do not recognize the P/N which is taken from the AIRBUS A320 AMM.  Help, anyonme. I would porefer to find it in Europe if possible.


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Fuel quantity vs. range
I'm just a Flight Simulator player with no real-life flying experience, so I apologize in advance if I'm asking a stupid question :)
I watched a TV show and saw that certain courier companies (DHL for example) tend to have multiple shorter flights with refueling instead of one long flight with larger initial amount of fuel, because in that way they burn less fuel.
Then I started thinking about the relation of fuel quantity and the range of an aircraft. On one side, the more fuel an airplane has, the longer range it will have. On the other side, more fuel means more weight, which will then increase the fuel consumption (but both the weight and the consumption rate will decrease gradually during the flight). Of course, let's observe a theoretical case, where the plane has constant speed and altitude, and there is no wind.
Is there any equation/graph for a certain aircraft type which shows how much fuel is "too much", i.e. if there is a "sweet spot" which will give the best ratio of fuel consumption and flight range?

Related if not duplicate : When are multiple hops more efficient than single leg?


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What is the lowest RNP approach requirement without being RNP AR?
I was recently told by a friend that as soon as RNP for an approach is below the 1.0/0.3nm standard that it is required to be RNP AR.
At least here in Australia, a curved segment anywhere on the approach will qualify it as RNP AR, even if the RNP is 1.0/0.3nm.
Is there a hard and fast rule for RNP AR?

I feel like this subject of RNP could use a Wiki for disambiguation.  You could ask this question in 10 different ways.  Ie "What is the difference between RNP AR and RNP 0.3?" would be one.

In ICAO DOC 9905 (Required Navigation Performance Authorization Required Procedure Design Manual) you can find the following definition in Chapter 2.1

RNP APCH versus RNP AR APCH
2.1.1 RNP APCH is defined as an RNP approach procedure that requires a lateral TSE of +/-1 NM in the initial,
  intermediate and missed approach segments (MAS) and a lateral TSE of ±0.3 NM in the FAS. Guidance on
  implementing RNP APCH operations can be found in the PBN Manual, Volume II, Chapter 5, Implementing RNP APCH.
2.1.2 RNP AR APCH is defined as an RNP approach procedure that requires a lateral TSE as low as ±0.1 NM
  on any segment of the approach procedure. RNP AR APCH procedures also require that a specific vertical accuracy be
  maintained as detailed in the PBN Manual, Volume II, Part B, Chapter 6. The datum crossing point (DCP) for RNP AR
  procedures is the point located above the landing threshold point (LTP) or the fictitious threshold point (FTP). The RNP
  AR APCH criteria apply only to those aircraft and operators complying with specified additional certification, approval
  and training requirements. RNP AR APCH procedures are only published where significant operational advantages can
  be achieved while preserving or improving safety of operation. The RNP AR certification and approval requirements are
  contained in the PBN Manual. For the purposes of applying the criteria contained in this manual, RNP AR procedure
  obstacle protection is associated with RNP navigation accuracy requirements. The RNP navigation accuracy
  requirement is used to determine the area semi-width value (in NM) of a protection area associated with a segment of an
  instrument procedure.

So, yes, any procedure below the 1.0/0.3 NM standard is defined as RNP AR.
You will not normally find curved segments (RF turns) on an RNP APCH chart, as these segments require a recent FMS as noted in ICAO DOC 8168 Vol. II Part III Appendix to Chapter 5.

Note 5.— RF may only be used for RNP procedures flown by aircraft equipped with systems that are compatible with ARINC 424-17, or later.

In those cases the chart will be promulgated with RF required.

Exactly the answer I was looking for, the ICAO DOCs scare the hell out of me!

There appears to be an "RNP APCH" spec, an "RNP AR" spec, and also and "RNP 0.3" spec.  What does this RNP 0.3 spec imply then?


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Is there a way to see what aircraft are based out of an airport?
Is there a software solution to determining what aircraft spend the majority of their downtime at an airport?
Or perhaps aircraft with journeys that start and stop at a particular airport more than 60% of the time.

I am actually asking about one specific airport in Australia. It will be 80% GA.

What do you mean by a "software solution"?  Because you could easily call the flight schools and airport manager to determine the number of hangars and tiedowns rented out.  Or go there and count if you are local. If you are just looking for a number... and for one specific airport.  It might take a bit more effort to compile a list of registration numbers if that's what you are looking for.  More clarity is needed.

And you are interested in the GA aircraft or in the airliners?

If the aircraft have ADS-B, then you may be able to track them that way. A service like ADS-B Exchange tracks aircraft using volunteer feeds. While it doesn't directly show where aircraft are most often, it wouldn't be too difficult to adapt the data for that.
Even better, you can set up an ADS-B receiver of your own near the airport, and do whatever you like with the data.
If the aircraft don't have ADS-B, there isn't really any practical software way to track them.


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When a parallel runway is closed at an uncontrolled field, does the notation change for the operating runway?
I’m currently a CFI/CFII/MEI at a flight school based out of Falcon Field (KFFZ.) Falcon has a pair of runways, 4/22 R/L. When the tower closes, runway 4L/22R is closed.
During a training event this afternoon while approaching the airport (after CT closure,) the student (a new hire CFI) made pattern calls appropriately, however, would state “left downwind runway four,” etc. He stated that a previous instructor had “chewed him out” in the past for saying “runway four right” after the parallel runway had closed. The student in the backseat, who had a different instructor, corroborated the information and stated he was taught the same.
My initial reaction was: that’s ridiculous. The designation of a runway doesn’t change simply because the parallel is temporarily closed. However, my inner instructor wants to find some kind of actual reference to support an answer.
Has anyone heard of, or learned this,  before? And if so, do you have a reference? I‘ve never heard of this before and was curious if anyone here has. Any information would be appreciated, if you’ve even heard of such a thing.

The runway doesn't disappear because the tower closes, it makes no sense to act like it does.

What could have been the worst aviation disaster on US soil AC759 approach SFO came within feet of occurring because pilot confused parallel taxiway w/parallel runway. If it ain't decommissioned and plowed under, it's still there, so designate L/R. Interestingly, that "incident" did not meet FAA reporting requirements, but someone did the right thing.

I would suggest that instead of asking us for supporting evidence, ask those who claim that this is correct. i.e. talk to the new CFI and the student in the backseat to support their claims. Have them get back with their instructors, if necessary, to find some regulation to support their assertion.

I would write to the local GADO and get an opinion from them, without naming names or slagging anybody, just present the circumstances and ask the proper way to do it.

@GdD - That was precisely my point to them. Thanks!

@FreeMan, typically this would be my course of action. And I did indeed have them reach out to their instructors for reference. However, I was writing more to determine if anyone else had heard of this and if so could they cite where. I was fairly confident in my personal analysis. Thanks!

It might be more clear to ask "When a parallel runway is closed when the tower is closed"--the term "uncontrolled field" is arguably ambiguous but the FAA uses the term uncontrolled airport to mean an airport in uncontrolled (Class G) airspace, not an airport with no operating control tower. If the (srfc) airspace at KFFZ happened to be designtd to revert to Clss E rather than G when the tower was closed, as is the case at many other airports, would this have any real impact on the basic thrust of your question? I think not.Thus the reference to an "uncontrolled field" seems superfluous.

@Cether, ask them what would then happen if 22L were closed for maintenance, leaving only 22R open (and the tower open or closed) ? Does that now make the right runway "22" ? Do they think that might not introduce some confusion if on a given day, "22" might be the left or right runway? How long does a runway have to be closed before the remaining runway gains standalone designation ?

There is no guidance that runway/tower closure status should change the name of a runway in the AIM, Airplane Flying Handbook, 7110.65, or anything else I've ever read. If such guidance exists somewhere, it's not well publicized.
And as you said, the alleged guidance would make no sense at all. In the situation you describe at Falcon Field, calling "runway four" is potentially ambiguous. But calling "runway four right" is never ambiguous: in the harshest possible analysis it's simply redundant. Redundancy is clearly preferable to ambiguity (indeed, something that eliminates ambiguity is by definition not redundant) and so there is no intelligible rationale to the other instructors' claims.

This was my explanation to the candidate/student as well. It simply isn’t logical to ignore the closed runway, and I could find no evidence to the contrary either. Thanks!
@StephenS I was confident there was no evidence. My question was more to determine if anyone had heard of this, and if so, could they cite where. I’m confident in my own evidentiary discovery, and I’m fact absence of evidence is just fine with me.

@Cether Fair enough, thanks for clarifying.

Reminds me of the trouble Air Canada 759 had landing at SFO runway 28.

@Harper-ReinstateMonica, that's what I said, 28R

The "chewing out" instructor is an deeply misguided and a danger to his students: a runway's name is basically permanent. It can be changed, but everything associated with it, like approach plates, runway signage, facilities directories, etc all change at the same time.
Regularly, one parallel runway is closed for months for construction - basically rebuilding it. And the NOTAMs all remind you, for months on end, that "RWY 01L/19R CLSD" and operations continue on 1R/19L. Which keeps its name, unchanged, even though it is the airport's only open runway on the 1/19 orientation.
Whatever that CFI was promoting about the sole open runway being renamed twice daily is wrongheaded and foolish. One might wonder how he thinks the big long strip of pavement parallel to the operating runway should be referred to... did it suddenly become "Taxiway Zulu" when it closed as a runway? (You got a NOTAM or AFD reference for that?)  Or is it still 4L, like the paint at its southwest end says? In which case, read out loud what it says on the runway to its right...
Or imagine the case of parallel approaches: if the open runway is now suddenly "runway 4", and I'm cleared for the ILS to "runway 4", should I use the frequency from the approach to the runway-formerly-known-as-4R, or for the other ILS-to-runway-4-something?  Because even when the runway is closed, an approach to it can still be available for use with side-step or circling mins!  (And while the pilot can be expected to know all the closure NOTAMS for all the airports he might use, his FMS and paper Jepp charts are still going to have "4R" and "4L" but nothing for just "4".)
No, that CFI was so wildly far off base it may be hard to find a one sentence statement that "no, we don't rename runways each time a parallel runway closes or reopens." But a cursory consideration of actual practice makes it perfectly clear that that's not what happens. If this "instructor" is actually griping at students over this, a sitdown with a chief instructor or an ASI (i.e. a Fed) would be in order -- he has betrayed his responsibility to teach the material he has been entrusted with.


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Relation between lift force and torque produced in propeller used for vertical take-off and landing aircrafts
There are many answers for this question but none of them are specific.
I need to find the exact relation between the lift force of a propeller of specific pitch, attack angle , dimensions and material with torque to be produced in a propeller at a specific speed at a certain altitude of a vertical take-off and landing aircraft to hover and fly forward.
Can some experts in the field derive this relation.

There are too many variables to catch this in one equation, there is some background in this answer and in this one

Plus - some experts in the field have derived the many equations describing this, notably Prouty (Helicopter Performance, Stability & Control) and Leishman ( Principles of Helicopter Aerodynamics.)  In the first couple of chapters, you will find that rotor diameter, blade profile, blade twist, blade AoA, forward speed, altitude and a few other parameters are involved. In other words: your question is very broad.

What you are looking for is Blade Element Theory:

The expression for the torque of the whole propeller is therefore
$$ Q = \frac{1}{2} \rho V^2 B \int_0^RQ_c \, dr $$

Q - total torque required by propeller
p (rho) - density of atmosphere the propeller is acting in
V - free stream velocity (aka velocity of airplane w.r.t air)
B - number of blades on propeller
R - radius of propeller
Qc - Torque required by a segment of a propeller blade at dr
dr - small delta of radius

Qc is the force dF (see fig.2) of the section dr that we are calculating for, multiplied by the radius R at which the section is located.

fig.2
As we can see from the figure, dF is the total aerodynamic force (lift + drag) of the section of the propeller blade dr we are calculating for, projected onto the plane of the propeller. df can thus be calculated by the equation:

where:

ф = arcsin(V/(2*pi/n)) is the angle of the travel of blade with respect to air
V - freestream velocity
n - rpm
 - angle between the lift component and the resultant aerodynamic force dR (*note - should be dD/DL)
 dL and dD are calculated the same as for a wing profile. (*note - be sure to use correct lift and drag coefficients Cl and Cd at alpha = beta - ф)

Can you explain what the terms in the equation mean and how to apply this formula?

The equation boils down to Q = Q.

@Koyovis that's like saying F=m*a boils down to F=F... well yeah, but that's an oversimplification.

What is the  relation between lift force L and torque Q?

@Koyovis A propeller is essentially a rotating wing. When it rotates, each section of each blade, produces lift and drag. The vector formed by summing L + D of a section of a blade, and projecting onto the plane (disk) of the propeller, forms a force acting against the rotation of the propeller. The sum of these forces along the length of each blade, multiplied by the radius at which these forces are acting, is the total torque required to turn the propeller.

Sorry. I missunderstood your last question. I will update the answer a bit later today

The relationship of torque produced by the engine and lift force will be the drag of the rotor.  Increase in lift force by increasing rpm or AOA will require a proportional increase in power output from the engine.  Air density also plays a role.
With a common helicopter, torque is counter balanced by increasing or decreasing torque of the tail rotor.

Thanks for replying @RobertDiGiovanni, Can you please put that into a formula considering all proportionality constants and what if an electric motor is used to drive the rotor?

@Mohammed Siddique using an electric motor is a good idea.  Starting on a small scale, power input, lift and torque are easily measured.

Well, I am designing a Motor and, i have calculated the Lift force to be produced by the rotor, i just need to figure out how much torque does my motor should produce to achieve that lift. Can you help me @RobertDiGiovanni.

Not without knowing the lift/drag ratio of the airfoil you are using for your rotor.  Depending on the drone, you may be able to "reverse engineer" from existing drones (at the hobby store).

How is lift/drag ratio depends on torque!? Can you explain me a little further. @RobertDiGiovanni

The lift/drag ratio of the rotor.  It is a spinning wing.

Yeah! I don't know, how to explain you but "how much torque and speed does my propeller need to generate to get the expected lift/drag... " Can you please state the answer for this question in mathematical form!?... Or do you know any website to learn this specific concept!... Please give me the formula for this or if there's nothing like it... explain me why or give me a website name which will explain me this question! @RobertDiGiovanni

@Mohammed Siddique Well, appreciate that we can keep working on it.  The formula for lift and drag are similar:  all have same rho (air density), same Area, same velocity (squared)  Lift = area x rho x V$^2$ x coefficient of lift (or drag of prop).  Coefficient is airfoil type at a given Angle of Attack (and so is Drag).  Once you have those values, you know how much rotor torque there will be (as with a helicopter).  Then you know how much counter torque is required by the tail rotor.  Try Airfoil Tools for starters on the net.

treat your rotor as a rotating airfoil.  The average drag as expressed over its length (remember V$^2$!) will be its torque.  Because of V$^2$, the rotor angular momentum "sweet spot" is not halfway between each end (but can be controlled by varying AOA along the blade).  Look at a windmill.

that is center of drag load can be controlled by varying AOA along blade

Thank you so much! @RobertDiGiovanni. Now, i can proceed with my work full-fledged.


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Is there a cockpit indication if the B737 flap load relief is not working properly?
On a 737, does the pilot get any cockpit indication that his Flap Load Relief is not working properly? Say for instance due to a Flap Lever Position Switch failure?

By what sequence of cause & effect do you expect a failure of a switch related to the position of the flap handle to manifest itself as a failure of the Load Relief system? The latter system doesn't do anything until you're about to overspeed the flaps (so, it activates pretty rarely), but a problem with the flap lever should be obvious during normal operations.

The cockpit indication would be that the flaps don't retract as expected. The subsequent flap overspeed would then be captured by the Flight Data Recorder, the same as any other exceedance. But I'm unaware of any specific indication on a cockpit display that indicates directly "the Flap Load Relief isn't working".

If a (minimal) flap skew is detected, all 737 will display a 15 degree difference in flap position.
If the automatic flap load limitation engages, a FLAP LOAD RELIEF light illuminates right above the flap gauge. The limiter is on all 737, the light only on some types.

Can you document this? Can't recall ever seeing such a "Flap Load Relief" light ever mentioned in the manuals I've seen.   Separately, what does the first sentence about skew have to do with the OP's question?

@RalphJ The FLAP LOAD RELIEF light exists in my 737 NG FCOM, but it is listed as an option. However, it illuminates when flap load relief occurs normally, not when there is a problem with the flap load relief system, so this doesn't really answer the question.


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As a general rule, must the cg of a tandem ultralight be greater than 25% mean aerodynamic chord?
As a general rule, must the cg of a tandem ultralight ( Re 500k-1,000k) be greater than 25% mean aerodynamic chord?
I understand the centre of pressure of a classic wing is at it's quarter point. It also produces a nose down moment, so that the cg and/or and horizontal tail moment need to offset this, or the plane will dive.
To provide a nose up moment, the horizontal tail must produce a tail down force.
If you want a tandem airplane, you want the exact opposite.
So the to provide a nose up moment, I would imagine you want the cg always behind the Cp ( 25% MAC) of the wing, but in front of the plane neutral point, as you want to the tail to provide an offsetting tail up force,(nose down moment)
Is this correct?

you want the cg always behind the Cp (25% MAC) of the wing, but in front of the plane's neutral point, as you want the tail to provide an offsetting tail up force

Yes, that is correct. The cg should be between the forward wing's quarter point and the common neutral point (NP) of both wings. However, if you want some agility when maneuvering the plane, it should be much closer to the neutral point. If both wings are of equal size, you definitely want the rear wing to contribute some lift. Since it flies in the downwash of the forward wing, it will see a smaller change in effective angle of attack and have a smaller lift curve slope, which already supplies some stall margin by helping to let the forward wing stall first. By shifting the cg a bit forward of the NP (10% to 25% of MAC should be sufficient), you will reduce lift on the rear wing further and increase stability.

I understand the centre of pressure of a classic wing is at it's quarter point.

Only if the wing has a symmetric or reflex airfoil. With regular cambered airfoils the cp is further aft and moves forward to the quarter point with increasing angle of attack.

I don't think it's correct to say that downwash "supplies some stability". It supplies "safety", but by itself it reduces the pitch moment slope and hence stability.

@Zeus: Agreed. But it does not reduce stability - the downwash only shifts the neutral point forward, away from the geometric mean of the quarter points of both wings.

Technically yes; some prefer to say "pitch stiffness" for this.

@Zeus: Interesting. For me, aerodynamic stiffness is proportional to and caused by dynamic pressure.

That's apparently not standard, but I found this usage in Etkin, and this is a popular textbook. He argued (correctly) that this term (the pitch moment slope) is not sufficient to describe stability per se, so he called it "stiffness", similarly to any other similar first-order term (like for a spring).

@Zeus: Yes, that makes sense. Stiffness against AoA change.


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Why did the Bede Bd5 have strakes on the horizontal tail?
Why did the Bede Bd5 have strakes on the horizontal tail?
Is it a sexy way of adding horizontal tail volume or reducing the span of the horizontal tail by increasing it's chord?

Strakes on the tail are usually there to account for some unwanted tendency, like uncommanded Dutch Rolls or similar.  I am looking for a clear picture of strakes and are not seeing any. Do you have a reference?  https://www.airspacemag.com/history-of-flight/thrill-flying-worlds-smallest-jet-180952134/

They work like large vortex generators to delay flow separation on the underside when the stabilator is at high (leading edge down) angles at low speed.  IIRC, the BD-5 had stabilator stalling issues during development.  That's one way of doing it.  Another way is to put VGs along the underside leading edge.
The Cessna Cardinal had a similar problem when it first entered service and Cessna's fix was to put LE slots in (a famous Service Bulletin known as the Cardinal Rule, with a comprehensive fleet mod campaign for the initial 500 or so aircraft), more or less for the same effect.

And I thought the Caravan was the only mess that required VGs on a tail surface!  (https://aviation.stackexchange.com/a/50000/23223).

Why would the tail stall? Too much aspect ratio?  Horiz. tail looks pretty slender.  It looks to me there was not enough chord so the tail was flying outside of it's Re range. Is that correct? Or was it downwash from the wing, or other?

@Fred those sound like separate questions, you should ask them in the proper format.

A stabilator tends to get a little closer to stalling AOA when fully aircraft nose up than a fixed stab/elevator.  Extend flap to increase the strength and angle of the downwash, add a little sideslip so that air is flowing across and down at the root, and you can exceed stall AOA at the root.  The Thorp T-18 had a stabilator stalling issue with full flap and side slip and would pitch over in a very annoying way, at the worst time, so Thorp told builders to limit flap to the second last notch.  I have seen T-18s with the same sort of strakes added by owners but couldn't find a pic on line.


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Is a 20% forced transition in xfoil similar to adding a vg?
Is a 20% forced transition etc. in xfoil similar to adding a vg?
I understand a 20% forced transition in xfoil, is tripping the boundary layer from laminar to turbulent.  Isn't that what a VG does?
A classic shaped naca foil like 2415, has a max cl of 1.5.  I understand that vg's usually add a cl of about 0.5-0.7.
So... if I force a transition to turbulent at about 15-20% of chord in xfoil, shouldn't the max cl of a classic foil go up from 1.5 to about 2?
It doesn't....?!?

No
It is more like putting a turbulator (such as a trip wire) there. Vortex generators will create a small vortex (hence the name) which puts much more energy into the boundary layer. XFOIL has no mechanism for simulating vortex generators.
Adding a forced turbulent transition will weaken the boundary layer downstream of its natural transition point, so it will tolerate less pressure rise. I assume you put them on the upper side: Now the airfoil will stall a bit earlier (at a lower angle of attack and lift coefficient).
15-20% is an unusual location for a turbulator, especially on the upper side. Their best location depends on the Reynolds number and the pressure distribution. On gliders, they make most sense on the lower side at around 80% of chord. On the upper side they might help a bit in part of the polar when placed at around 50%.

Ok great. Can one model a working slat in Xfoil?  How about Javafoil?

For a multi-element airfoil there is MSES. If you need to do the job of a van, don't pick a bicycle.


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Low speed, low wing loading?
Just looked at the Lamac ( light aircraft manufacturers association of Canada) specs.  If I remember correctly, They want to see a maximum of 3 psf wing loading for Vc of 60mph, rising to a maximum of 12psf for Vc of 120mph and above.
Why only 3 psf?  Looks to me they just want standard wings with a cl max of 1.5.
The Zenith 701 stol has a wing loading of about 10 psf, yet has a Vc of about 60mph, with a cl of about 3.

It's a design standard to set minimum wing area for the airplane's intended speed range using "unassisted" Clmax as the basic parameter. And most low speed wings have a Clmax without enhancement of somewhere around 1.5/1.6.
The 701 gets its low speed range with small wings using both slats and slotted full span flaps to get its 3+ Clmax, so it doesn't really fall within the definition.

I assume they want larger wing area at slower speed for safety?  With a partially stalled smaller wing, there is more chance of a crash.  Is this correct?

Not more chance of a crash, just that there is more energy which can to put you in the hospital for a longer stay. Traditionally the "safety" of ultralights has always depended on the low energy of the potential crash making up for very unreliable 2 stroke engines. Ironically the biggest danger of very low loading ultralights is actually because of the low mass/large area;when the engine quits they tend to just stop (well not quite) and you have to aggressively nose down to maintain airspeed.Stall spin accidents on climbout when the rotax wingy-dingy thing stops wingy-dingying is the big one.


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Polars for multi element foils?
Where can I find polars for multi element foils?
Unless I missed them, couldn't find any on airfoiltools.com
Is there a family of multi-element foils like Naca,or Selig, etc.?

Your question is too general. It would be more helpful if you specify the flight conditions and the types of aircraft that you are interested in. For instance, give us a range for the Reynolds number.
However, I have a fast answer for both high and low Reynolds. For high Reynolds ($Re \geq 10^6$), NLR-7301 (main and flap) and MDA (slat, main and flap) are airfoils for which you can find published experimental and numerical results (NASA, AGARD, etc.). For low Reynolds numbers ($Re < 10^6$), there are really not many experimental results that I know of. In fact, I was once lucky enough to find an airfoil catalog of F.X. Wortmann (printed format and in German) that had aerodynamic results for some fowler flap airfoils. Also, during my diploma thesis, I worked on an aerodynamic method for the fast analysis of multielement low Reynolds airfoils (based on XFOIL) and thus I used my method to analyze certain multielement low Reynolds number airfoils that I designed (starting from the S1223 airfoil of Selig). The document can be found here but it is written in Greek. Nevertheless, you can check the figures (NLR-7301 is also included in my study and you may trace the relevant references for further info).

You don't happen to have a scan of that airfoil catalog, do you? Hard data on Wortmann profiles is not easy to come by, even considering the UIUC work.

Unfortunately not. I found the catalog in an old (almost abandoned) library of a laboratory room of my previous university. I may contact a friend and ask him if he still works there, then I could ask him to take some photos/scan.

Sounds not worth the hassle, for a curiosity at best, but if it somehow falls into your hands, please digitize it for the greater good :)


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What are typical naca foils for winglets for ultralights/LSA?
What are typical naca foils for winglets for ultralights?

There are ultralights with winglets?  They are only really effective on airplanes that cruise at low indicated airspeed where the vortices are strong enough to give an energy recovery benefit that exceeds the weight/drag penalty of the winglet itself.  Which is, mostly, airplanes that cruise above 30000ft   And maybe, gliders.

Winglets are used on hangliders, trikes, the original ultralight - the lazier, velocity pusher aircraft, and most of all: birds, which is where the idea came from in the first place.  I'm thinking a NACA 009, although I've seen lot's of winglets that don't seem to be foils, just plates.

The Lazair has a kind of turned up wing tip, no so much a winglet.  The velocity and it's kin are using them as yaw stability surfaces (tip rudders) more than winglets.  Some hang gliders and sailplanes use them, because they fly in a speed range that is able to exploit the energy in the vortice.  Remember that a winglet is a sail. It makes lateral lift, producing an outwash that weakens the circulation around the tip and also generates a forward thrust component. Winglets on a jet point outboard slightly to optimize AOA. Since they are sideways lift makers, you need to use a cambered airfoil.

They are only worth using when induced drag is the dominant factor.  As soon as you speed up, other types of drag predominate and the induced drag benefit is cancelled out by the form drag of the winglet. Unless you are optimizing your ultralight/LSA for best L/D close to the stall, which is desirable for soaring aircraft, they are a waste of time because you pay for it at the high speed range.

Winglets are very common on ultralights and trikes, and have been so for more than a decade. http://www.airtrikes.net/wings.shtml  They have been found to improve longitudinal stability in straight and level flight, much as the effect of dihedral http://www.aeros.com.ua/news.php?lang=english&id=144. For winglet airfoils used it's a challenge to find out. You might have to email individual manufacturers.

The information I have, is that you would want to have the thinnest symmetrical airfoil, that will work in the specified Re range, eg. NACA009